Plasma treated metallized film

ABSTRACT

A plasma treated metallized plastic film is provided with super high barrier properties at substantially low cost.

RELATED APPLICATIONS

The present application claims the priority of U.S. ProvisionalApplication Ser. No. 60/403,294 filed on Aug. 14, 2002, and the priorityof U.S. Provisional Application Ser. No. 60/448,859 filed Feb. 21, 2003,both of which are fully incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to metallized films, particularly for usein the food and liquid packaging and decorative balloon industries.

BACKGROUND OF THE INVENTION

The present invention relates generally to various types of metallizedplastic films. Metallized plastic films are known in the art, and areused to provide barriers between the interior and external environmentof a package or product. Such barriers can be used, for example, forfood and liquid packaging or for decorative balloons. In the case offood and liquid, the barrier provided by the film packaging safeguardsthe enclosed product against the major causes of loss of food freshnessand flavor, namely, oxygen or water vapor flow into the package and/orexposure to ultraviolet light. Similarly, in the case of balloons, thebarrier protects against undesirable loss of gas caused by diffusionthrough the film and out of the balloon, such diffusion resulting inshrinkage and short balloon life.

Various clear plastic films were introduced for use as flexible foodpackaging in the early sixties. Such clear films, for example, wereprinted and laminated with polyethylene as an inner layer in the packagethat is also used for sealability. However, due to the fact that clearplastic film lacks sufficient gas and moisture barrier characteristicsneeded for proper packaging requirements, metallized film wassubsequently introduced in approximately the early seventies. Theprocess of metallization takes place in a vacuum chamber where a metal(e.g. pure aluminum), is melted, evaporated and deposited onto thefilm's surface. In the case of aluminum, for example, the vapor isdeposited on the substrate surface leaving a very thin coat of aluminummetal (e.g. 10-1000 Angstroms) that is enough to seal the surface poresof the substrate. The deposited metal improves the barrier properties bypreventing the transmission of oxygen and water vapor from the outsideenvironment to the inside of the package, or so forth.

Subsequently, further technology was developed involving modification ofthe chemical composition of the metallizable surface. These surfacepolymer modifications enhance moisture and gas barriers in addition toimproving metal adhesion, and are atmospheric treatments (includingcorona, flame, chemical, and plasma treatment), which result in directoxidation of the web surface. Most of the surface treatments aredesigned to modify the top surface of the polymer composition and not topenetrate into the bulk of the material. The greatest care must beexercised to determine which method of surface modification is best foreach type film to meet the final required properties of the product.

The various surface treatments have two major disadvantages, however.First, the treatment values are found to decrease with time from themoment that treatment of the surface is complete to the time ofmetallization in the vacuum chamber. As the rolls are stored in thewound form, the surface energy will decrease due to the diffusion ofsome chemical groups into the surface of the film. In addition, theadditional processes involved in the surface treatment add to the finalprice of the film.

Accordingly, it would be advantageous in the art to provide an improvedtreatment method and an improved metallized product which is simple andinexpensive to manufacture, and which provides increased barrierproperties. It would be further advantageous to provide a method whichcan be employed on plain film, and which provides the advantage of thevarious surface treatments, without dissipation, and at lower cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a packaging filmthat is capable of providing enhanced barrier properties to oxygen andwater vapor transmission.

It is an object of the present invention to provide a packaging filmthat is capable of providing enhanced barrier properties to ultravioletlight.

It is a further object of the present invention to provide packagingfilm with improved barrier properties which is simple and inexpensive tomanufacture.

In accordance with the the present invention, a plasma metallized filmis provided, particularly for the food and liquid packaging and balloonindustries, wherein the film is provided with improved barriercharacteristics over prior films in the art while being simple andinexpensive to manufacture. In one preferred embodiment, a method isprovided in which a plastic film is subjected to plasma treatment insidethe vacuum chamber of a metallization apparatus and is coated on one orboth surfaces of the treated film with a desired coating material (e.g.aluminum vapor). Further to the process and reaction conditionsdisclosed herein, a film is produced exhibiting excellent oxygen andmoisture barrier properties. Due to these increased barrier properties,shelf life and the floating time can be extended dramatically whilemaintaining the aesthetic appeal of the metallized film, a strongadvantage in merchandising food and decorative balloon products.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, a method is provided forproviding a film having improved barrier properties. In particular, thefilm provides an improved barrier to oxygen and water vaportransmission, and to ultraviolet light. Further in accordance with theinvention, an improved barrier is provided, while providing a methodwhich is simple to implement and resulting in a film which is relativelyinexpensive to manufacture. In preferred embodiments, the film can beused in the food and liquid packaging industries, or for decorativeballoons.

In accordance with the method of the invention, a user will generallybegin with plastic in roll form, with the thickness, width and length ofthe sheet of plastic on the roll varying according to the user'sultimate needs. For example, the initial film can be of polyester,polypropylene, polyethylene, polyvinyl chloride or nylon. For processingof the initial film into a desired treated form, the film is processedin a vacuum system machine which is used to deposit the coating materialonto the film. In a preferred embodiment of the invention, the apparatusused for metallization of the film is a Galileo Vacuum System machine,and further preferably a Galileo Mega2 Model, such as the Mega 4-2410B.However, while the present invention will be described herein withrespect to use of the latter machine as an illustration of a preferredembodiment, it will be understood that the present invention is notintended to be limited to such a machine or to the preferred embodimentsdisclosed herein, as other vacuum metallization machines can be used aswell.

In a vacuum system metallization apparatus, various components areprovided for processing and metallization of the film, including, forexample, the winding system, the vacuum chamber, the pumping system,controls, evaporation system, etc. The rolls of plastic are fed throughthe winding system portion of the machine, which includes the drivesystem, the tension control, and so forth. The vacuum chamber is theportion of the machine where a vacuum is produced for use during thecoating process, and which has the evaporators for evaporation of thecoating material into a gas for deposition onto the film. Pumping of gaswithin the machine is accomplished by the pumping equipment.

The roll of film is set up inside of the metallization machine on asection referred to as “the unwind shaft”, where the film is unwound offof the roll for passage through the remainder of the machine. From theunwind shaft, the film is threaded through the machine for it toeventually pass through the plasma treater over some additional rollersand through the evaporation zone until it reaches the empty core of therewind shaft (the rewind station). This process begins with setup of theclear roll in the winding system section. After the setup is complete,the machine is dosed and hermetically sealed for commencement of thepumping down process. During pumping down, all air and gases are removedfrom the vacuum chamber until reaching a desired high state of vacuum(preferably in the 10⁻⁵ mbar range, and 7.0×10⁻⁵ mbar, for example, in apreferred embodiment).

Once the machine has reached vacuum pressure, plasma treatment can beconducted. As discussed above, plasma treatment involves modification ofthe surface of the plastic film, and is used to promotes adhesion of thecoating material (e.g. a metal) to the film's surface. In addition,plasma treatment can enhance the moisture and gas barrier properties ofthe resulting metallized film. Within the plasma treater, high voltagepower (preferably 7-25 KW), a high magnetic field and a gas mixture areprovided. Preferred operating conditions for producing desiredmetallized films in accordance with the present invention, inconjunction with various film materials, are provided in Table 1 below.

The essential feature of the plasma treatment is that it supplieshigh-energy electrons in sufficient quantities to generate heavy ions,with electrons being added from the gas blend for bombardment of thefilm surface. In accordance with the invention, a preferred gas blendfor use in the plasma treatment is a mixture of 80% Nitrogen and 20%Argon (“Gas B” of Table 1, also referred to as “Plasma B”).Alternatively, a gas blend of 30% Oxygen and 70% Argon, or 50% Oxygenand 50% Argon can be used. Further alternatively, one or more of thegases Argon, Nitrogen and/or Oxygen can be used, whether individually aspure gases or as a mixture in any combination suitable for the desiredapplication. Or, other gases may be used for treatment of the filmsurface providing that they are suitable to provide the desired finalcharacteristics of the film achieved herein.

When the plasma generator is in use, ions and electrons are constrainedin the magnetic field above the generator where the film is passedthrough. Also, some systems can be magnetically enhanced to open thefield lines toward the film by placing permanent magnets behind the filmas it passes through the treater. Those permanent magnets have theeffect of directing the ions and electrons toward the film surface.

The electrical system in conjunction with the gas blend fed into theplasma treater will clean and activate the film surface for chemicalmodification. This change in the surface characteristics occurs justprior to the deposition of the coating material (e.g. aluminum vapor).It is believed that oxygen species are generated on the film surfaceunder the metal layer resulting in oxidized surfaces. That oxygen iseither added to the surface by the gas or is drawn to the surface fromthe polymer itself.

The plasma treater is provided in an area within the machine which islocated before the evaporation zone, and which is sealed from theevaporation zone. After passing through the plasma treater, the film ismoved into that evaporation zone. Isolation of the plasma treater fromthe evaporation zone is provided so that the gas from the plasma treaterwill not interfere with the evaporation process.

After treatment of the film with the plasma treater, the plasma treatedfilm moves into and through the evaporation zone, where the evaporatorsmelt and evaporate the coating component to be applied to the film. Inthe evaporation zone, solid coating material is fed into the evaporators(e.g. aluminum wire or any other desired coating material), and as theevaporators heat up to reach the desired temperature (e.g. 1400 degreescentigrade in the case of aluminum) the coating material is vaporized.

Although the process of the present invention can be conducted at anydesired rate, in a preferred embodiment the machine is simultaneouslyactivated to pump out gas to reach the desired vacuum pressure, whilepower is provided to the plasma treaters and the evaporators are heatedto the necessary temperature, before beginning to move the film withinthe machine. This allows the film to be rapidly and efficiently movedthrough the entire machine from section to section once the varioussections of the machine are ready, without needing to wait in onesection for a subsequent section to be available for use. Generally, itis necessary to wait several minutes until the coating material has beenfed into all of the evaporators (also known as “boats”), and until thatmaterial has filled all of the pores in the ceramic and begun tovaporize uniformly before beginning a run of film through themetallization machine. In other words, preferably the evaporators arewarmed up and all of the boats in the line are stabilized prior toinitiating treatment of the film with the plasma treater, so that thefilm can pass from the plasma treater into the evaporation zone andonward without delay.

Thus, it is in the evaporation zone that the plasma treated film comesinto contact with the coating material. The temperatures for theevaporators depend on the material to be evaporated. In a preferredembodiment, pure aluminum is evaporated for deposit on the film, e.g. attemperatures beginning from approximately 1400 degrees Centigrade (1400°C.). In alternative embodiments, silver or gold or tin or other metals,or glass (as a silica) could be utilized. Accordingly, while aluminum isgenerally referred to in the illustrations herein as an example of apreferred embodiment, it is to be understood that the present inventionis not limited to such preferred material.

In the evaporation step, coating material molecules travel throughoutthe evaporation zone in a vacuum. To produce the desired vacuum, pumpingequipment is provided in communication with the evaporation zone toimprove the coating process within that zone. For example, in the caseof aluminum, it is important that the aluminum not come into contactwith any oxygen molecules, since pure aluminum is to be deposited on thefilm, with the presence of any aluminum oxide being highly undesirable.Similarly, aluminum can boil and evaporate more efficiently at the lowerpressure. The vacuum also facilitates the free travel of the aluminummolecules to provide an even coat from one edge to another of the film,such that dark and light areas are not produced on the film. Inaddition, the pumping out of oxygen helps avoid damage to the ceramicevaporators, since the presence of oxygen molecules around those hightemperature evaporators (running at approximately 1400° C. or higher)will degrade the evaporators and decrease their effective life.

Within the vacuum, the aluminum comes into contact with the surface ofthe plastic film, which may pass over a chill roller. The chill rolleris a roller maintained at a sufficiently low temperature to maintain thedimensional stability of the plastic film when it is exposed to theexcessive heat of the vapor, and further preferably to maintain the filmat a sufficiently low temperature to promote condensation of thealuminum thereon. For example, while the vapor may be approximately1400° C., the film may be approximately 70-80 degrees Fahrenheit.

Although a chill roller is needed for those films which are verysensitive to heat, a chill roller is not essential for the process. Somefilms resist heat and therefore do not need special cooling. With thosefilms, the ambient temperature of the film or the cold temperature ofvacuum can itself provide a sufficient temperature difference to causecondensation, and the movement of the film at a rapid line speed resultsin insufficent time for the film to melt. Likewise, the film does notneed to be supported by the chill roller during the evaporation, butrather can be free spanning, i.e. metallized while running between tworollers. When the film is free spanning, it can be cooled after theevaporation step, if desired, using a chill roller or by a coolingtower.

When the coating material vapor comes into contact with the film on theroller it condenses on the film's surface. Upon contact, both a chemicalbonding and physical bonding occurs between the aluminum and the film. Acoat of material is thereby provided on the substrate in the sufficientthickness to seal the surface pores of the substrate. In the preferredembodiment, a coating of, for example, 120-200 or more preferably,10-1000 Angstroms is used, although any other desired thickness may beemployed if desired. For example, a greater coating thickness may beused in the embodiments utilizing multiple coating layers on one or bothsides of the film to further reduce transmission through the material,i.e. to increase the barrier properties, albeit at higher cost.

After deposition of the aluminum on the film, the film is rewound on theempty core, producing the finished roll. After the roll is complete, thepumping valves are closed, power is turned off of the evaporators, andan inlet air valve is opened to put more air into the machine to reachatmospheric pressure. At that point, the machine is opened and thefinished roll can be removed.

Generally, the amount of improvement in the barrier properties and metaladhesion depends on the reaction conditions, including, for example, thegas in use, the blend ratio and the flow rate. Thus, in accordance withthe present invention, reaction conditions have been developed whichoptimize the barrier properties produced in accordance with theinvention. The preferred reaction conditions for producing improvedmetallized films with various film types in accordance with theinvention, are shown in Table 1 as follows: TABLE 1 Reaction Conditionsfor Plasma Metallization Process Flow/s Line speed Drum Optical Filmtype Gauge MOS/MBS Gas cm3/s Power ft/M temp. Vacuum Density Nylon 40MOS B 500 10 KW 1400 −4 F. 7.0E−005 2.6 mbar Nylon 48 MOS B 500 10 KW1400 −4 F. 7.0E−005 2.6 mbar Nylon 40 Mbar S B 500 10 KW 1400 −4 F.7.0E−005 3.7 mbar PET/Plain 48 MOS B 500 12 KW 1850 −4 F. 7.0E−005 2.2mbar PET/Chem. 48 MOS B 500 12 KW 1975 −4 F. 7.0E−005 2 mbar PET/Chem.48 MOS B 500 12 KW 1100 −4 F. 7.0E−005 3 mbar OPP 70 MOS B 500 12 KW1100 −4 F. 7.0E−005 3 mbar

Accordingly, further to the invention, a highly effective film isproduced at decreased cost. In general, a saving of at least 15% can beachieved by metallizing a plain film with the plasma treatment methodsof the present invention rather than using a film with a specialformulation. Tables 2 and 3 below, for example, shows a comparison ofsome common values that can be produced using the present invention,followed by some typical values for barrier properties of pastmetallized and clear products at 0.5 mil: TABLE 2 Oxygen transmissionrate (OTR) (reported in cc/100 in²/day at 75° F. and 50% RH) Plasmatreated and metallized on both sides .0035 or less (in accordance withthe present invention) Plasma treated metallized on one side  .01-.025(in accordance with the present invention) Metallized PET film .05-.08Metallized OPP .06-1.0 Clear PET film 7-9 Clear OPP  95-130 Clear Nylon  2-3.8

TABLE 3 Water vapor transmission rate (WVTR) (reported in gr/100 in²/day@ 100° F. 100% RH) Plasma treated and metallized on one side .008-.015 (in accordance with the present invention) Metallized PET film .05-.1 Clear PET film 2.8 Clear OPP film .5-1.0 Clear Nylon 7-11

In a further preferred embodiment of the invention, a three-zonegeometry is used (as is available, for example, in the Galileo Mega2).In this embodiment, in-line surface treatment (i.e. plasma treatmentwithin the metallization machine) takes place in the first zone. Thisallows the surface of the film to be cleaned of imperfections andimpurities and prepared for better metal adhesion, and thus, improvedbarrier performance, all in-line. Metallizing takes place in a secondvacuum zone, and can be conducted at a line speed as fast as 3,000 fpm.Due to the multi-zone geometry, the machine can achieve and maintain avacuum in the 10⁻⁵ mbar range, which improves metal density and preventsspit holes. Furthermore, the Mega 2 machines can deposit aluminum formicrowave applications as well as for complete opacity. The web iscooled in the third vacuum zone, where it is possible to maintain theweb's temperature within two degrees, even at a high level of metaldeposition. This cooling system allows running of plastic films that areheat sensitive and extensible. Furthermore, as a result of thethree-zone system, a different vacuum level can be maintained in each ofthe three zones if desired. For example, a higher degree of vacuum canbe maintained in the evaporation zone than in the winding zone, where ashigh a level of vacuum is not necessary.

Further factors which can be used to modify the barrier characteristicsof the film, include adjustment of the process to conduct plasmatreatment and metallization on one or both sides of the film or both(“Surface A” and/or “Surface B”) and/or to conduct one or more passes oneach side. Thus, while exemplary results can be obtained using just onepass at metallization, further passes of metallization can be used toincrease the barrier properties resulting, albeit at higher cost.

In one such series of embodiments, for example, one side of thesubstrate film can be metallized (“Metal One Side” or “MOS” of Table 1),with the film plasma treated on one or or both sides of the film(surface A or B). For example, the substrate film can be plasma treatedon a surface of the film (surface A or B) and metallized on that plasmatreated side in one pass. Or, the substrate film can be plasma treatedon surface A or B, and then metallized on that plasma treated surface,and then remetallized again on that metal side (two pass). Or, thesubstrate film can be metallized on surface A or B (before any plasmatreatment), then plasma treated on that metallized side, thenremetallized again on that plasma treated metal surface (two pass). Or,the substrate film can be plasma treated on surface A or B, and thenmetallized on the plasma treated surface, then plasma treated again onthat metallized side, and remetallized again on the plasma treatedmetallized surface (two pass).

In a further series of embodiments, both sides of the substrate film canbe metallized (“Metal Both Sides” or “MBS” of Table 1). For example, thesubstrate film can be plasma treated on both surfaces A & B, and thenmetallized once on each surface (one pass each side). Or, the substratefilm can be plasma treated only on one surface (surface A or B) andmetallized on both surfaces (one pass each side). Or, the substrate filmcan be plasma treated on both surfaces A & B, with side A and side Beach metallized once, then plasma treated again on one side, andremetallized for a second time on that same side (one pass side A andtwo pass side B). Or, the substrate film can be metallized on bothsurfaces A & B (before any plasma treatment), then surface A or surfaceB can be plasma treated, followed by remetallization for a second timeover that plasma treated side (one side one pass, the second side twopass). Or, the substrate film can have surface A just metallized andsurface B both plasma treated and metallized, followed by surface Bbeing plasma treated again and remetallized for a second time (one passsurface A and two pass surface B). Or, the substrate film can havesurface A both plasma treated and metallized, and surface B initiallyjust metallized, followed by surface B being plasma treated (on thatmetallized surface) and then remetallized for a second time (one passsurface A and two pass surface B).

Similarly, any further number or combination of plasma treatments and/ormetallizations on either or both sides of the film can be conductedconsistent with the present invention.

Accordingly, in accordance with the invention, a super high barrierplasma treated plastic film (e.g. polyester, polypropylene,polyethylene, polyvinyl chloride or nylon) is provided that ismetallized on one or both surfaces of the film, and which can be used,for example, for food or liquid packaging or for decorative balloons, atlow cost. The oxygen transmission rate (OTR) through the treated filmachieved via the invention is less than 0.01 cc/100 in²/day and thewater vapor transmission rate (WVTR) is reduced to 0.02-0.35 or even toless than 0.02 gr/100 in²/day at 100° F./100% RH, depending on theselected substrate.

For example, with nylon the oxygen transmission rate (OTR) is reducedfrom 0.07 cc/100 in²/day with prior art methods to 0.015 cc/100 in²/day.For nylon MBS, the OTR is reduced from 0.070 cc/100 in²/day to 0.0025cc/100 in²/day. For polyester, the OTR is reduced from 0.050-0.070 to arange of 0.015-0.030 cc/100 in²/day. The water vapor transmission rate(WVTR) also was reduced from 0.070-0.100 gr/100 in²/day at 100° F. and100% RH to 0.020-0.035 gr/100 in²/day. For example, with OPP WVTR wasreduced from the normal 0.050 gr/100 in²/day to as low as 0.015 gr/100in²/day at 100° F. and 100% RH. The metal adhesion bond was alsoincreased using the invention from 250 gr/in to 400-500 gr/in.

Furthermore, the choice of using one or two sides for metallizationand/or plasma treatment, and of conducting plasma and/or metallizationtreatment one time or multiple times (whether twice, three times ormore), can be made to yet further increase the barrier properties of theinvention to whatever extent desired. Such variations are highlyeffective, albeit at increased cost. Accordingly, while the barrierproperties listed above are typical values produced at relativelyinexpensive cost, an even more impermeable barrier can nonetheless beachieved, if desired, in accordance with the invention.

The metallized film preferably has a thickness in the range of 0.20 milto 10 mil where the thickness is chosen depending on the desiredstiffness of the package needed for the final product. In one of thepreferred embodiments, that metallized film is further comprised ofplain plastic film, the film being plasma treated on one or bothsurfaces and metallized on one or both surfaces of the film. Also, thesubstrate surface of the film may be chemically or corona treated priorto plasma treatment or metallization, using known methods. For example,chemically treated SP91 film or SP95 film can be utilized, as availablefrom SKC Materials, Inc. of Covington, Ga. The gases used for the plasmatreatment can be Argon, Nitrogen and/or Oxygen at various ratios, orother desired gases.

Having described this invention with regard to specific embodiments, itis to be understood that the description is not meant as a limitationsince further modifications may suggest themselves, or may be apparentto those in the art. It is intended that the present application coverall such modifications and improvements thereon.

1-80. (canceled)
 81. A method comprising the steps of: providing a material for use in food or liquid packaging, said material comprising a plastic film, said plastic film having been subjected to plasma treatment inside the vacuum chamber of a metallization apparatus, said plastic film having been coated on at least one side with a desired metal to form a metallized plastic film, said metallized plastic film comprising an oxygen transmission rate (OTR) of no greater than 0.03 cc/100 in²/day, and a water vapor transmission rate of no greater than 0.035 gr/100 in²/day at 100° F. and 100% relative humidity (RH), and wherein said plasma treatment uses a mixture of at least two gases selected from the group comprising: Nitrogen, Argon, and Oxygen.
 82. A method as claimed in claim 81, wherein said metal is aluminum.
 83. A method as claimed in claim 81, wherein said metal is silver.
 84. A method as claimed in claim 81, wherein said metal is gold.
 85. A method as claimed in claim 81, wherein said metal is tin.
 86. A method as claimed in claim 81, wherein said plastic film comprises polyester.
 87. A method as claimed in claim 81, wherein said plastic film comprises polypropylene.
 88. A method as claimed in claim 81, wherein said plastic film comprises polyethylene.
 89. A method as claimed in claim 81, wherein said plastic film comprises polyvinyl chloride.
 90. A method as claimed in claim 81, wherein said plastic film comprises nylon.
 91. A method as claimed in claim 81, wherein said plasma treatment uses a mixture of Nitrogen and Oxygen.
 92. A method as claimed in claim 81, wherein said plasma treatment uses a mixture of Nitrogen and Argon.
 93. A method as claimed in claim 81, wherein said plasma treatment uses a mixture of 80% Nitrogen and 20% Argon.
 94. A method as claimed in claim 81, wherein said plasma treatment uses a mixture of Oxygen and Argon.
 95. A method as claimed in claim 81, wherein said plasma treatment uses a mixture of 30% Oxygen and 70% Argon.
 96. A method as claimed in claim 81, wherein said plasma treatment uses a mixture of 50% Oxygen and 50% Argon.
 97. A method as claimed in claim 81, wherein said oxygen transmission rate is between 0.01 and 0.03 cc/100 in²/day.
 98. A method as claimed in claim 81, wherein said oxygen transmission rate is no greater than 0.010 cc/100 in²/day.
 99. A method as claimed in claim 81, wherein said oxygen transmission rate is no greater than 0.0035 cc/100 in²/day.
 100. A method as claimed in claim 81, wherein said oxygen transmission rate is no greater than 0.0025 cc/100 in²/day.
 101. A method as claimed in claim 81, wherein said water vapor transmission rate is between 0.02-0.035 gr/100 in²/day at 100° F. and 100% RH.
 102. A method as claimed in claims 1, wherein said water vapor transmission rate is no greater than 0.02 gr/100 in²/day at 100° F. and 100% RH.
 103. A method as claimed in claim 81, wherein said water vapor transmission rate is no greater than 0.015 gr/100 in²/day at 100° F. and 100% RH.
 104. A method as claimed in claim 81, wherein said plastic film has been metallized on one side of said plastic film.
 105. A method as claimed in claim 81, wherein said plastic film has been metallized on both sides of said plastic film.
 106. A method as claimed in claim 81, wherein said plastic film has been plasma treated on one side of said plastic film.
 107. A method as claimed in claim 81, wherein said plastic film has been plasma treated on both sides of said plastic film.
 108. A method as claimed in claim 81, wherein said plastic film has been metallized at least twice on at least one side of said plastic film.
 109. A method as claimed in claim 81, wherein said plastic film has been plasma treated at least twice on at least one side of said plastic film.
 110. A method as claimed in claim 81, wherein said plastic film has been metallized at least twice and plasma treated at least twice.
 111. A method as claimed in claim 81, wherein said plastic film has been plasma treated on a first side of said plastic film and has been metallized on said first side.
 112. A method as claimed in claim 81, wherein said plastic film has been plasma treated on a first side of said plastic film, followed by metallization on said first side, followed by metallization again on said first side.
 113. A method as claimed in claim 81, wherein said plastic film has been metallized on a first side of said plastic film, followed by plasma treatment on said first side, followed by metallization again on said first side.
 114. A method as claimed in claim 81, wherein said plastic film has been plasma treated on a first side of said plastic film, then metallized on said first side, then plasma treated again on said first side, then metallized again on said first side.
 115. A method as claimed in claim 81, wherein said plastic film has been plasma treated on both sides of said plastic film and metallized on both sides of said plastic film.
 116. A method as claimed in claim 81, wherein said plastic film has been plasma treated on a first side of said plastic film, and has been metallized on both sides of said plastic film.
 117. A method as claimed in claim 81, wherein said plastic film has been plasma treated and metallized on a first side and a second side of said plastic film such plasma treatment and metallization being conducted once in any order, followed by plasma treatment again on said first side, followed by metallization again on said first side.
 118. A method as claimed in claim 81, wherein said plastic film has been metallized on both a first side and a second side of said plastic film, followed by plasma treatment on said first side, followed by metallization again on said first side.
 119. A method as claimed in claim 81, wherein said plastic film has been metallized on a first side of said plastic film and both metallized and plasma treated on a second side of said plastic film, followed by a second plasma treatment and second metallization on said second side, said second plasma treatment and second metallization being conducted in either order.
 120. A method as claimed in claim 81, wherein said plastic film has been both plasma treated and metallized on a first side of said plastic film, and metallized on a second side of said plastic film, followed by plasma treatement on said second side, and metallization again on said second side. 